Chapter 9 Behavioral Design Patterns

1
Chapter 9Behavioral Design Patterns
2
Process Phase Affected by This Chapter
Requirements Analysis
Design
Architecture
Framework
Detailed Design
Implementation
Key
secondary emphasis
main emphasis
x
x
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Design Purpose
Interpreter
Interpret expressions written in a formal grammar.
Design Pattern Summary
Represent the grammar using a Recursive design
pattern form Pass interpretation to aggregated
objects.
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Interpreter Client Interface
AbstractExpression interpret()
Client
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Interpreter Design Pattern
1..n
AbstractExpression interpret()
Client
TerminalExpression interpret()
NonTerminalExpression interpret()
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Interpreter Sequence Diagram
Client
AbstractExpression
NonterminalExpression
NonterminalExpression
interpret()
...
create interpret()
...
TerminalExpression
...
create interpret()

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Example of a Virtual Machine Program
400Mhz 128MB
assemble .
260Mhz 64MB
260Mhz 32MB
Graphics reproduced with permission from Corel.
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Input For Network Assembly Example
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Output of Network Assembly Example (1 of 3)
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Output of Network Assembly Example (2 of 3)
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Output of Network Assembly Example (3 of 3)
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Design Goal At Work ? Flexibility ,
Correctness, Reuse ?
Separate the processing of each part of the
network order.
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Interpreter Design Pattern
Client
Component assemble()
component1
NetSystem assemble()
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Application of Interpreter Design Pattern
0..1
Component assemble()
Client
1
component1
NetSystem assemble()
component2
cpu
CPU describe()
Setup getInputFromUser() parse()
Computer assemble()
RAM describe()
ram
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Key Concept ? Interpreter Design Pattern ?
-- a form for parsing and a means of processing
expressions.
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Purpose of Iterator

• - given a collection of objects
  e.g.,
• the videos in a video store
• a directory
• - having specified ways to progress through them
  e.g.,
• list in alphabetical order
• list all videos currently on loan
• ... encapsulate each of these ways

Aggregate object
iterator2
iterator7
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Design Purpose (Gamma et al)
Iterator
Provide a way to access the elements of an
aggregate object sequentially without exposing
its underlying representation.
Design Pattern Summary
Encapsulate the iteration in a class pointing (in
effect) to an element of the aggregate.
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Using Iterator Functions
/ To perform desiredOperation() on elements of
the aggregate according to the iteration (order)
i / for( i.setToFirst() !i.isDone()
i.increment() ) desiredOperation(
i.getCurrentElement() )
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Functions for Iterator
// Iterator "points" to first element void
setToFirst() // true if iterator "points" past
the last element boolean isDone() // Causes
the iterator to point to its next element void
increment() // Return the element pointed to by
the iterator C getCurrentElement()
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Iterator in Arrays, Vector, and in General
Iterator Operations Iterator Operations Iterator Operations Iterator Operations
Set to beginning Increment Get current element Check not done yet
The Iterator Index (integer) i on array myArray i 0 i myArray i i lt myArray .length
The Iterator Index (integer) j on Vector myVector j 0 j myVector .get( j ) j lt myVector .size()
The Iterator Iterator (object) myIterator myIterator .setToFirst() myIterator .increment() myIterator .getCurrent Element() ! myIterator .isDone()
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Imagining Iterator
Key Intended sequence of Element objects
element Element
Aggregate of Element objects
After first() executes, iterator references this
object.
iterator Iterator
Before increment() executes, iterator references
this object.
After increment() executes, iterator references
this object.
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Iterator Example Setup Code
// Suppose that we have iterators for forward
and // backward order we can re-use
print_employees() List employees new
List() ForwardListIterator fwd // to go from
front to back new ForwardListIterator (
employees ) ReverseListIterator bckwd // to go
from back to front new ReverseListIterator
( employees ) client.print_employees( fwd )
// print from front to back client.print_employ
ees( bckwd ) // print from back to front
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Iterator Class Model
Client
Iterator setToFirst() increment() isDone() getCurr
entItem()
Aggregate
1n
ConcreteIterator
ConcreteAggregate
AggregatedElement
1
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An Organizational Chart Example
Vanna Presley vice president, 4 years
Sue Miller svce. mgr., 7 years
Sal Monahan svce. mgr., 1 year
Sam Markham svce. mgr., 5 years
Iolanthe Carp ind. contrib., 8
Inge Carlson ind. contrib., 12
Inez Clapp ind. contrib., 11
Inky Conway ind. contrib., 6
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Iterating by Organizational Seniority Over a Bank
Organization
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Iterating by Years of Service Over an
Organization Chart
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Design Goal At Work ? Flexibility , Correctness
?
Separate the visiting procedure from the
processing of individual employees.
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Class Structure for Iterator Example
Client
Setup
OrgChartIteratorDP
OrgChartDP
OrgChartIterator first() next() isDone() currentIt
em()
Employee display()
Teller
ServiceIterator
Supervisor
OrgSeniorityIterator
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Computing next()
DeepRoot
root
doneNode
( 1 )
( 0 )
1
2
3
6
4
5
7
8
10
11
9
12
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( 1, 2, 0, 0 ) // my distance from the end of my
sibling list )
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Sequence Diagram for Encounter Foreign Character
Use Case
User
Employee
Setup
main()
AlphabeticalOrgChartIterator
Get org chart as in Composite example tbd
OrgChartIterator
Client
getTheIterator()
display( OrgCharIterator )
first(), next(), idDone(), getItem() etc.
Employee
display()
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Computing next()
DeepRoot
distance from the end of my sibling list
root
doneNode
( 1 )
( 0 )
1
2
3
( 1, 2 )
4
5
6
7
8
( 1, 2, 0 )
9
10
11
12
( 1, 2, 0, 0 )
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Iterator Example Sequence Diagram
User
Employee
AlphabeticalOrgChartIterator
Setup
main()
OrgChartIterator
Client
Get org chart as in Composite example tbd
getTheIterator()
display( OrgCharIterator )
first(), next(), isDone(), getItem() etc.
Employee
display()
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Iterator in the Java API
Iterator next() hasNext() remove()
Collection Iterator iterator()
ListIterator
List
AbstractCollection
Iter
AbstractList ListIterator listIterator()
ListItr
ArrayList
Vector
IBM implementation
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Output for Iteration on a Java ArrayList
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Address Book Application Using Java Iterator
Collection Iterator iterator()
Iterator next() hasNext() remove()
List
ListIterator
AbstractList ListIterator listIterator()
ListItr
ArrayList
Key
This application
0..n
NameAddrEntry
AddressBook
Java API
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Iterator Class Model
Iterator setToFirst() increment() isDone() getCurr
entItem()
Aggregate createIterator( )
Client
OLD
ConcreteAggregate createIterator( )
ConcreteIterator
return new ConcreteIterator( this )
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Output for StringTokenizer Example
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Key Concept ? Iterator Design Pattern ?
-- to access the elements of a collection.
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Solicitation of Customer Information 1 of 2
Name and Location
Basic information
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Solicitation of Customer Information 2 of 2
Account Information
Customer ID
Total business
Amount due
Additional information
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Design Purpose
Mediator
Avoid references between dependent objects.
Design Pattern Summary
Capture mutual behavior in a separate class.
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The Mediator Class Model
Mediator
Colleague
ConcreteColleague1
ConcreteColleague2
ConcreteMediator
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1. Initiation by ConcreteMediator
ConcreteColleague1
ConcreteColleague2
ConcreteMediator
doPart1()
Mediator Sequence Diagrams
doPart2()
2. Initiation on a ConcreteColleague
Mediator
mediate()
mediate()
doSome1()
doSome2()
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Design Goal At Work ? Reusability and
Robustness ?
Avoid hard-coded dependencies among the games
GUI classes, enabling their use in other contexts.
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Application of Mediator To Customer Information
Application
CustomerDisplay
CustomerGUI
BasicInfoGUI
CustTypeDisplay
CustInfoDisplay
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The Mediator Class Model in the Java API
ComponentListener actionPerformed()
Component addComponentListener()
MyComponent1
MyComponent2
MyEventListener
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Key Concept ? Mediator Design Pattern ?
-- to capture mutual behavior without direct
dependency.
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Observer
Design Purpose
Arrange for a set of objects to be affected by a
single object.
Design Pattern Summary
The single object aggregates the set, calling a
method with a fixed name on each member.
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Observer Design Pattern
Server part
Client part
Client of this system
1
Source notify()
Observer update()
1..n
2
for all Observers o o.update()
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Observer Design Pattern
Server part
Client part
Source notify()
Observer update()
Client
1
1..n
2
for all Observers o o.update()
ConcreteObserver observerState update()
ConcreteSource state
3
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Observer Applied to International Hamburger Co.
Server part
Client part
Client
1..n
Observer update()
Source notify()
SeniorManagement forecast update()
Headquarters demand
Marketing marketingDemand update() doDisplay()
if( abs( hq.demand - marketingDemand ) gt 0.01 )
marketingDemand hq.getDemand() doDisplay()

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I/O Example for Mutual Fund Observer Example
Note HiGrowthMutualFund starts with 3 shares of
Awesome, assumes price of 1.0, and has
non-Awesome holdings totalling 400.0 Note
MedGrowthMutualFund starts with 2 shares of
Awesome, assumes price of 1.0, and has
non-Awesome holdings totalling 300.0 Note
LoGrowthMutualFund starts with 1 shares of
Awesome, assumes price of 1.0, and has
non-Awesome holdings totalling 200.0 Enter
'quit' Any other input to continue. go on Enter
the current price of Awesome Inc. in decimal
form. 32.1 Value of Lo Growth Mutual Fund changed
from 201.0 to 232.1 Value of Med Growth Mutual
Fund changed from 302.0 to 364.2 Value of Hi
Growth Mutual Fund changed from 403.0 to
496.3 Enter 'quit' Any other input to
continue. go on Enter the current price of
Awesome Inc. in decimal form. 21.0 Value of Lo
Growth Mutual Fund changed from 232.1 to
221.0 Value of Med Growth Mutual Fund changed
from 364.2 to 342.0 Value of Hi Growth Mutual
Fund changed from 496.3 to 463.0 Enter 'quit'
Any other input to continue.
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Design Goal At Work ? Flexibility ?
Allow mutual funds objects to easily acquire or
divest of stocks.
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Observer Example Mutual Funds
Observable notifyObservers()
Observer update( Observable, Object )
MutualFund value numAwesomeShares
Setup
LongTermMutualFund . update()
AwesomeInc price
Client
MediumTermMutualFund . update()
HiGrowthMutualFund . update()
Java API Class
Key
Developer Class
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Observer in the Java API
Observable notifyObservers()
Observer update( Observable, Object )
MyConcreteObserver observerState update()
MyObservable
subject
Key
Developer Class
Java API Class
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Key Concept ? Observer Design Pattern ?
-- to keep a set of objects up to date with the
state of a designated object.
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Design Purpose
State
Cause an object to behave in a manner determined
by its state.
Design Pattern Summary
Aggregate a State object and delegate behavior to
it.
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State Design Pattern Structure doRequest()
behaves according to state of Target
targetState.handleRequest()
Client
Target doRequest()
TargetState handleRequest()
targetState
1
TargetStateB handleRequest()
TargetStateA handleRequest()
. . . . . .
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GUI For a Role-Playing Video Game
Set Characteristics
Courtesy Tom VanCourt and Corel
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Design Goal At Work ? Correctness and
Reusability ?
Separate the generic code for handling button
clicks from the actions which depend on the
games status at the time.
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State Design Pattern Applied to Role-Playing Game
MyGame setCharacteristics()
MyGameState handleClick()
state
state.handleClick()
Engaging handleClick()
SettingUp handleClick()
Waiting handleClick()
SettingCharacteristics handleClick()
showWindow() . // more
showWindow() . // more
// already responding // display
message
// do nothing // display message
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Key Concept ? State Design Pattern ?
-- to cause a objects functions to behave
according to the state its in.
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Chain of Responsibility
Design Purpose
Allow a set of objects to service a request.
Present clients with a simple interface.
Design Pattern Summary
Link the objects in a chain via aggregation,
allowing each to perform some of the
responsibility, passing the request along.
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Chain of Responsibility Object Model
entryHandlerHandlerSubclassX
(next element) HandlerSubclassZ
successor
successor
(next element) HandlerSubclassY
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Chain of Responsibility Class Model
Handler handleRequest()
Client
successor
HandlerSubclassA handleRequest() respondA()
HandlerSubclassB handleRequest() respondB()
. . . .
respondA() // handle some of the
required functionality successor.handleRequest()
// pass along remaining responsibility
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GUI For Customer Information Application
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Output for Customer Information Application
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Design Goal At Work ? Flexibility ?
Isolate the responsibilities of each part of the
input form to generate its XML.
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Class Model For User Information Collection
TextFieldListener client
CustomerInfoElement
container
Each of these classes supports handleClick()
CustomerPersonal
CustomerProfessional
CustomerAddress
Company
CustomerName
CompanyName
CustomerInfo
CustomerInfoApp setup
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Object Model Fragment for Customer Information
Example
container
CompanyName
container
Company
handleClick()
container
CustomerProfessional
handleClick()
CustomerInfo
handleClick()
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Key Concept ? Chain of Responsibility Design
Pattern ?
-- to distribute functional responsibility among
a collection of objects.
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Design Purpose
Command
Increase flexibility in calling for a service
e.g., allow undo-able operations.
Design Pattern Summary
Capture operations as classes.
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The Command Design Pattern
Client
Command execute()
replaced
Target1 action1()
Action1Command execute()
Action2Command execute()
Target2 action2()
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The Command Design Pattern Example
command
MenuItem handleClick()
Command execute()
document.cut()
command.execute()
CutCommand execute()
document
Document cut() copy()
document.copy()
CopyCommand execute()
document
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Sequence Diagram for Document Command Example
MenuItem
command Command
CopyCommand
document Document
handleClick()
execute()
copy()
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I/O for Word Processor Undo Example1 of 2
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I/O for Word Processor Undo Example2 of 2
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Design Goal At Work ? Flexibility and Robustness
?
Isolate the responsibilities of the Word
Processor commands, making them save-able and
reversible.
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Undo Example Class Model
Command execute() undo()
WordProcessor
commandHistory
0..n
document
Document text String
DocumentCommand getInputFromUser()
document
CutCommand textCut String offset int
execute() undo()
PasteCommand offset int length
int execute() undo()
QuitCommand execute()
UndoCommand execute()
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Key Concept ? Command Design Pattern ?
-- to avoid calling a method directly (e.g., so
as to record or intercept it).
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Example of Template Motivation

• Required to solve equations of the form
• ax2 bx c 0.
• Must be able to handle all input possibilities
  for a, b, and c.
• This is a tutorial application that must
  provide full explanations to users about the
  solutions for all values for a, b, and c.

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A Basic Quadratic Algorithm

1. Report progress
2. Display number of solutions
3. Display first solution, if any
4. Display second solution, if any

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Design Purpose
Template
Allow runtime variants on an algorithm.
Design Pattern Summary
Express the basic algorithm in a base class,
using method calls where variation is required.
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Class Model for Template
Client
TemplateAlgorithm handleRequest() nonInheritedMeth
od() calledMethod1() calledMethod2() .
algorithm
Subject doRequest()
algorithm.handleRequest()
Algorithm1 calledMethod1() calledMethod2() .
Algorithm3 calledMethod1() calledMethod2() .
Algorithm2 calledMethod1() calledMethod2() .
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I/O For Quadratic Example 1/2
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I/O For Quadratic Example 2/2
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Quadratic Display Algorithm
displaySolutions() displayWhatsHappening() di
splayNumSolutions() displayFirstSolutions()
displaySecondSolution()
Override
Override
Override
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Design Goal At Work ? Flexibility and Robustness
?
Isolate the main algorithm for quadratic solution
display. Isolate the variants that depend on the
coefficients.
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Class Model for Quadratic Problem
Client
Setup getABC()
QuadraticAlgorithm displayWhatsHappening() display
Solution() inputMakesSense() displayNumSolutions()
displayFirstSolution() displaySecondSolution()
QuadraticEquation float a, b, c solveQuadratic()
algorithm
algorithm.displaySolution()
NoSolutions displayNumSolutions() displayFirstSolu
tion() displaySecondSolution()
OneSolution displayNumSolutions() displayFirstSolu
tion() displaySecondSolution()
TwoSolutions displayNumSolutions() displayFirstSol
ution() displaySecondSolution()
InfinitelyManySolutions displayNumSolutions() disp
layFirstSolution() displaySecondSolution()
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Key Concept ? Template Design Pattern ?
-- to capture a basic algorithm and its variants.
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Summary of Behavioral Patterns

• Behavioral Design Patterns capture behavior among
  objects
• Interpreter handles expressions in grammers
• Iterator visits members of a collection
• Mediator captures behavior among peer objects
• Observer updates objects affected by a single
  object
• State allows method behavior to depend on current
  status
• Chain of Responsibility allows a set of objects
  to provide functionality collectively
• Command captures function flexibly (e.g.
  undo-able)
• Template captures basic algorithms, allowing
  variability

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